image/ImgDrawResult.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef mozilla_image_ImgDrawResult_h
   7 #define mozilla_image_ImgDrawResult_h
   8
   9 #include <cstdint>  // for uint8_t
  10 #include "mozilla/Attributes.h"
  11 #include "mozilla/Likely.h"
  12
  13 namespace mozilla {
  14 namespace image {
  15
  16 /**
  17  * An enumeration representing the result of a drawing operation.
  18  *
  19  * Most users of ImgDrawResult will only be interested in whether the value is
  20  * SUCCESS or not. The other values are primarily useful for debugging and error
  21  * handling.
  22  *
  23  * SUCCESS: We successfully drew a completely decoded frame of the requested
  24  * size. Drawing again with FLAG_SYNC_DECODE would not change the result.
  25  *
  26  * SUCCESS_NOT_COMPLETE: The image was drawn successfully and completely, but
  27  * it hasn't notified about the sync-decode yet. This can only happen when
  28  * layout pokes at the internal image state beforehand via
  29  * StyleImage::StartDecoding. This should probably go away eventually, somehow,
  30  * see bug 1471583.
  31  *
  32  * INCOMPLETE: We successfully drew a frame that was partially decoded. (Note
  33  * that successfully drawing a partially decoded frame may not actually draw any
  34  * pixels!) Drawing again with FLAG_SYNC_DECODE would improve the result.
  35  *
  36  * WRONG_SIZE: We successfully drew a wrongly-sized frame that had to be scaled.
  37  * This is only returned if drawing again with FLAG_SYNC_DECODE would improve
  38  * the result; if the size requested was larger than the intrinsic size of the
  39  * image, for example, we would generally have to scale whether FLAG_SYNC_DECODE
  40  * was specified or not, and therefore we would not return WRONG_SIZE.
  41  *
  42  * NOT_READY: We failed to draw because no decoded version of the image was
  43  * available. Drawing again with FLAG_SYNC_DECODE would improve the result.
  44  * (Though FLAG_SYNC_DECODE will not necessarily work until after the image's
  45  * load event!)
  46  *
  47  * TEMPORARY_ERROR: We failed to draw due to a temporary error. Drawing may
  48  * succeed at a later time.
  49  *
  50  * BAD_IMAGE: We failed to draw because the image has an error. This is a
  51  * permanent condition.
  52  *
  53  * BAD_ARGS: We failed to draw because bad arguments were passed to draw().
  54  *
  55  * NOT_SUPPORTED: The requested operation is not supported, but the image is
  56  *                otherwise valid.
  57  */
  58 enum class MOZ_MUST_USE_TYPE ImgDrawResult : uint8_t {
  59   SUCCESS,
  60   SUCCESS_NOT_COMPLETE,
  61   INCOMPLETE,
  62   WRONG_SIZE,
  63   NOT_READY,
  64   TEMPORARY_ERROR,
  65   BAD_IMAGE,
  66   BAD_ARGS,
  67   NOT_SUPPORTED
  68 };
  69
  70 /**
  71  * You can combine ImgDrawResults with &. By analogy to bitwise-&, the result is
  72  * ImgDrawResult::SUCCESS only if both operands are ImgDrawResult::SUCCESS.
  73  * Otherwise, a failing ImgDrawResult is returned; we favor the left operand's
  74  * failure when deciding which failure to return, with the exception that we
  75  * always prefer any other kind of failure over ImgDrawResult::BAD_IMAGE, since
  76  * other failures are recoverable and we want to know if any recoverable
  77  * failures occurred.
  78  */
  79 inline ImgDrawResult operator&(const ImgDrawResult aLeft,
  80                                const ImgDrawResult aRight) {
  81   if (MOZ_LIKELY(aLeft == ImgDrawResult::SUCCESS)) {
  82     return aRight;
  83   }
  84
  85   if (aLeft == ImgDrawResult::NOT_SUPPORTED ||
  86       aRight == ImgDrawResult::NOT_SUPPORTED) {
  87     return ImgDrawResult::NOT_SUPPORTED;
  88   }
  89
  90   if ((aLeft == ImgDrawResult::BAD_IMAGE ||
  91        aLeft == ImgDrawResult::SUCCESS_NOT_COMPLETE) &&
  92       aRight != ImgDrawResult::SUCCESS &&
  93       aRight != ImgDrawResult::SUCCESS_NOT_COMPLETE) {
  94     return aRight;
  95   }
  96   return aLeft;
  97 }
  98
  99 inline ImgDrawResult& operator&=(ImgDrawResult& aLeft,
 100                                  const ImgDrawResult aRight) {
 101   aLeft = aLeft & aRight;
 102   return aLeft;
 103 }
 104
 105 /**
 106  * A struct used during painting to provide input flags to determine how
 107  * imagelib draw calls should behave and an output ImgDrawResult to return
 108  * information about the result of any imagelib draw calls that may have
 109  * occurred.
 110  */
 111 struct imgDrawingParams {
 112   explicit imgDrawingParams(uint32_t aImageFlags = 0)
 113       : imageFlags(aImageFlags), result(ImgDrawResult::SUCCESS) {}
 114
 115   const uint32_t imageFlags;  // imgIContainer::FLAG_* image flags to pass to
 116                               // image lib draw calls.
 117   ImgDrawResult result;       // To return results from image lib painting.
 118 };
 119
 120 }  // namespace image
 121 }  // namespace mozilla
 122
 123 #endif  // mozilla_image_ImgDrawResult_h